1. Field of the Invention
The present invention is directed to a method and circuit for monitoring a number of electrode surfaces of the neutral electrode of an HF surgery device to determine whether the surfaces are in planar adjacency against the body tissue.
2. Description of the Prior Art
In HF surgery devices, partial detachment of the neutral electrode can result in burning of the patient, and therefore methods and circuits are known to monitor the plurality of electrode surfaces (sub-electrodes) which are present as part of the neutral electrode to determine if those surfaces are in planar adjacency against the body tissue of the patient. In such known methods and circuits, a source current (auxiliary current) is applied to one of the electrode surfaces (auxiliary electrode) which is in contact with the body tissue of the patient in an electrically conductive fashion. The resulting current is measured at two other electrode surfaces, which are also in contact with the body tissue of the patient in an electrically conductive fashion. If one of the measured currents exceeds a permissible deviation toward a higher or lower current in comparison to the other electrode, an alarm signal is generated, which may automatically disconnect the surgery device. The permissible deviation may be exceeded, for example, due to partial detachment of an electrode surface from the patient. If, however, two electrode surfaces detach simultaneously so that the remaining surfaces of the respective electrodes in contact with the patient have approximately the same area, the resulting currents which are measured will still be approximately the same, and thus the monitoring circuit will not be able to determine that such partial detachment has occurred.
Solutions to this problem are known which attempt to minimize the risk of the formation of residual electrode surfaces of identical size occurring upon partial detachment of the neutral electrode. For example, the number of electrode surfaces may be increased and/or the electrode surfaces may be provided with a special shape. A disadvantage of all known methods and circuit arrangements, however, is that the auxiliary electrode itself cannot be used as an electrode which is monitored to determine the existence of detachment.